Light emitting apparatus with optical interference layer having a larger refractive index than a light emitting layer

ABSTRACT

A display apparatus includes on a substrate a plurality of light emitting elements in which an organic layer including a white light emitting layer is sandwiched between a lower transparent electrode and an upper electrode, and further includes a reflection layer and an optical interference layer provided between the light emitting elements and the substrate, wherein the optical interference layer is made of a material having a lower refractive index than the refractive index of the light emitting layer and the ratio (nr/nb) of a refractive index (nr) with respect to a red wavelength region to a refractive index (nb) with respect to a blue wavelength region is less than 0.95, and the orders of interference m for blue, green, and red wavelength regions are 5, 4, and 3, respectively, when the optical distance from the light emitting layer to the reflection layer is (2m+1)λ/4±(⅛)λ.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a Continuation of U.S. patent application Ser. No.15/786,478, filed Oct. 17, 2017, which claims the benefit of JapanesePatent Application No. 2016-206800, filed Oct. 21, 2016, each of whichis hereby incorporated by reference herein in their entirety.

BACKGROUND OF THE INVENTION Field of the Invention

The present disclosure relates to full-color display apparatuses using awhite light emitting element.

Description of the Related Art

In recent years, organic electronic elements using organic compoundswith which coating film formation and low-temperature processing can beperformed have been studied to take the place of electronic functionalelements using inorganic compounds. Especially, light emitting elementsincluding organic light emitting layers made of organic compounds, whichare also referred to as organic electroluminescent elements or organicEL elements, have been rapidly developed.

To realize full-color display, the display apparatus needs basic colors,red (R), green (G), and blue (B). In the case of using light emittingelements as a light source, there are various methods of obtaining thethree colors RGB. Examples include a method in which red-light,green-light, and blue-light emitting layers are separately applied and amethod in which RGB color filters are used to separate white light froma white light emitting element into separate colors. Recent full-colordisplay apparatuses include an increased number of pixels with amicronized pixel size. As it is difficult to micronize a high-resolutionmask and conduct highly-accurate alignment, use of the method ofseparately applying organic light emitting layers of three colors cancause a problem of a decrease in yield rate. On the other hand, themethod using a white light emitting element and RGB color filters iseffective for improving the yield rate because it does not requireseparate applications using masks. However, since the white lightemitting element emits a wide spectrum, which is a characteristic of anorganic material, it is difficult to increase color purity, and thisleads to a problem of a narrow color reproduction range. There is also aproblem of increased power consumption due to low emission efficiencycaused by low transmittance of the color filters.

Japanese Patent Application Laid-Open No. 2008-210740 (hereinafter,“Patent Document 1”) discusses an arrangement in which the distancebetween a light emitting layer and a reflection layer of a lightemitting element is set equal to a suitable distance for obtaining aresonance effect of red, blue, and green in order to improve colorpurity and facilitate productivity.

However, the display apparatus discussed in Patent Document 1 has aproblem of a significant color shift depending on a viewing angle.

SUMMARY OF THE INVENTION

The present disclosure is directed to a full-color display apparatuswith a white light emitting element which has an increased colorreproduction range, reduced power consumption, and decreased viewingangle dependency while the ease of production is realized.

According to an aspect of the present disclosure, a display apparatusincludes a substrate, a plurality of light emitting elements formed onthe substrate, a reflection layer provided between the substrate and thelight emitting elements, and an optical interference layer providedbetween the light emitting elements and the reflection layer, whereinthe plurality of light emitting elements include a transparent lowerelectrode, an organic layer including a white light emitting layer, andan optically transparent upper electrode in this order from thesubstrate side, wherein an optical distance from the white lightemitting layer to the reflection layer is equal in the plurality oflight emitting elements, wherein the optical interference layer has alarger refractive index than a refractive index of the white lightemitting layer and a ratio (nr/nb) of a refractive index (nr) withrespect to a red wavelength region to a refractive index (nb) withrespect to a blue wavelength region in the optical interference layer isless than 0.95, and wherein orders of interference m in the blue, green,and red wavelength regions are 5, 4, and 3, respectively, when theoptical distance from the light emitting layer to the reflection layeris (2m+1)λ/4±(⅛)λ.

Further features will become apparent from the following description ofexemplary embodiments with reference to the attached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view schematically illustrating a displayapparatus according to an exemplary embodiment.

FIG. 2 is an enlarged cross-sectional view schematically illustrating alight emitting element of the display apparatus illustrated in FIG. 1.

FIG. 3 is a graph illustrating fluorescent spectra of respective colorlight emitting dopants used in simulations.

FIG. 4 is a graph illustrating transmission characteristics of colorfilters used in simulations.

FIG. 5 is a graph illustrating electroluminescent (EL) spectra accordingto a first comparative example.

FIG. 6 is a graph illustrating EL spectra according to a secondcomparative example.

FIG. 7 is a graph illustrating EL spectra according to a thirdcomparative example.

FIG. 8 is a graph illustrating EL spectra according to a first example.

DESCRIPTION OF THE EMBODIMENTS

A display apparatus according to an exemplary embodiment of the presentdisclosure uses light emitting elements including a white light emittinglayer. The light emitting elements for blue, green, and red have thesame structure. The present exemplary embodiment is characterized inthat the optical distance from the light emitting layer to a reflectionlayer is optimized by the thickness of an optical interference layer sothat resonance effects are produced with respect to the respectivecolors and light of each color is emitted with high color purity.

The exemplary embodiment will be described below with reference to thedrawings. The dimensions of respective components illustrated in thedrawings are different from actual dimensions. Further, conventional andknown techniques in the art apply to portions that are not illustratedor described herein.

FIG. 1 is a cross-sectional view schematically illustrating a displayapparatus according to an exemplary embodiment. The display apparatus isa full-color, top-emission display apparatus. The display apparatusincludes a substrate 10 and a plurality of light emitting elements 2arranged in matrix on the substrate 10. Each of the light emittingelements 2 includes a transparent lower electrode (pixel electrode) 13,an organic layer 15, and an upper electrode 16 in this order from thesubstrate 10 side. Between the light emitting element 2 and thesubstrate 10 are provided a reflection layer 11 and an opticalinterference layer 12. An insulation layer (bank) 14 in FIG. 1 isolatesthe pixel electrode 13 from an adjacent pixel electrode 13.

In the present exemplary embodiment, since the top emission method isused in which light is extracted from an electrode located on theopposite side to the substrate 10, the substrate 10 can be a transparentor non-transparent substrate. The pixel electrode 13 and the upperelectrode 16 are provided with wiring (not illustrated) for supplyingpower thereto to cause emission of light. The organic layer 15sandwiched between the pixel electrode 13 and the upper electrode 16includes at least a white light emitting layer (not illustrated).Further, color filters 18R, 18G, and 18B which respectively transmit redlight, green light, and blue light are provided on the side of the lightemitting elements 2 from which light is extracted, whereby white lightemitted from the light emitting elements 2 is extracted outside thedisplay apparatus as red light, green light, and blue light. Thus, a redpixel 1R, a green pixel 1G, and a blue pixel 1B of the display apparatusaccording to the present exemplary embodiment have the same structureexcept for the color filters 18R, 18G, and 18B (for convenience, thecolor filters 18R, 18G, and 18B will be referred to as “color filter 18”hereinafter). A black matrix 19 in FIG. 1 blocks light between therespective color filters 18.

The reflection layer 11 is made of a highly-reflective metal such as analuminum alloy or silver alloy. The organic layer 15 needs to include awhite light emitting layer and can have a multilayer structure asillustrated in FIG. 2. For example, in the case where the pixelelectrode 13 is an anode, layers 15 a, 15 b, 15 c, and 15 d can be ahole transporting layer, a light emitting layer, a hole blocking layer,and an electron transporting layer, respectively. In addition to theselayers, an electron blocking layer, a hole injection layer, an electroninjection layer, etc. can be provided as needed in the organic layer 15.While the light emitting layer 15 b in FIG. 2 is a single layer, thelight emitting layer 15 b can be a white light emitting layer includinga plurality of layers each emitting a different color light. Theplurality of light emitting layers can be in contact with each other, orother layers can be provided between the plurality of light emittinglayers.

The upper electrode 16 is the optically transparent electrode located onthe side where light is extracted. The upper electrode 16 can be atransparent electrode such as an indium tin oxide (ITO) electrode or athin metal film. To improve color purity, use of a thin metal film witha high reflectance is desirable. In the case of using a thin metal film,a thin silver (Ag) alloy film containing an alkaline earth metal, suchas magnesium (Mg) or calcium (Ca), or elemental Ag can be used.

Desirably, a transparent sealing film 17 is provided on the upperelectrode 16 to prevent permeation of external oxygen and moisture tothe organic layer 15. The transparent sealing film 17 has the role ofprotecting the light emitting elements 2 not only from external oxygenand moisture but also from the process of forming the color filter 18.On the color filter 18 can be provided a transparent protectionsubstrate 20, such as glass or plastic, to protect the uppermostsurface.

The pixel electrode 13 is made of a transparent, conductive oxide suchas ITO or indium zinc oxide (IZO). White light emitted from the lightemitting layer 15 b and containing blue light, green light, and redlight passes through the pixel electrode 13 and produces opticalinterference between the light emitting layer 15 b and the reflectionlayer 11 and between the reflection layer 11 and the upper electrode 16.The optical distance from the light emitting layer 15 b to thereflection layer 11 and the optical distance from the reflection layer11 to the upper electrode 16 at this time can be adjusted such thatsimultaneous resonances (hereinafter, “multi-mode resonances”) occur inred, green, and blue wavelength regions, for example, at around 650 nm,530 nm, and 460 nm.

According to the present exemplary embodiment, the optical interferencelayer 12 for optical adjustment is made of a material which has a largerrefractive index than the refractive index of the light emitting layer15 b and in which the ratio (nr/nb) of the refractive index (nr) of thered wavelength region to the refractive index (nb) of the bluewavelength region is less than 0.95, for the following reason.

It is known that, in general, a resonance effect is produced when theoptical distance from the light emitting layer 15 b to the reflectionlayer 11 is (2m+1)λ/4. When the orders m are 5, 4, and 3, and blue,green, and red wavelengths represented as λb, λg, and λr, respectively,are assigned to the above-described condition, (11/4)λb, (9/4)λg, and(7/4)λr are obtained at which interference occurs to produce a resonanceeffect, and then in this condition, the following equation is likely tobe satisfied,(11/4)λb≈(9/4)λg≈(7/4)λr.For example, if the blue wavelength λb is adjusted to 440 nm, the greenand red wavelengths λg and λr can be caused to resonate at around 540 nmand 690 nm, respectively, which are peak wavelengths of green and red.Accordingly, a resonance mode (multi-mode resonances) having three peaksin blue, green, and red visible regions is generated. An error of ±(⅛)λis allowed in the optical distance regardless of an emission wavelength.More preferably, an error of ±( 1/16)λ is allowed.

Meanwhile, an optical distance is expressed as a product of refractiveindex×physical distance. Accordingly, a condition for obtaining aresonance effect based on the above-described condition is expressed as(11/4)λb=nb×d,(9/4)λg=ng×d, and(7/4)λr=nr×d,where nb, ng, and nr are respectively the refractive indexes for theblue, green, and red wavelength regions and d is the physical distancefrom the light emitting layer 15 b to the reflection layer 11, supposingthat the portion from the light emitting layer 15 b to the reflectionlayer 11 is made of a homogeneous material.Thus, (nr/nb)=( 7/11)×(λr/λb) is obtained by transforming the equations.

When the resonance wavelength of red is not less than 670 nm, visualsensitivity is decreased, and red luminance is decreased. This causes anincrease in power consumption. Thus, from the standpoint of powerconsumption, the resonance wavelength of red is desirably less than 670nm. Accordingly, λr<670 nm is satisfied if (nr/nb) is less than 0.95when λb=450 nm.

As illustrated in FIG. 1, the pixel electrode 13 and the opticalinterference layer 12 are provided between the light emitting layer 15 band the reflection layer 11, and the optical distance is the sum ofvalues obtained by respectively multiplying refractive indexes bythicknesses. However, as described above, the pixel electrode 13 is madeof ITO or IZO, and these materials having a high refractive index eachsatisfy (nr/nb)<0.95. Thus, according to the present exemplaryembodiment, if the optical interference layer 12 satisfies (nr/nb)<0.95,multi-mode resonances are produced in the desired wavelengths of blue,green, and red.

The light emitting layer 15 b is an organic material, so the refractiveindex of the light emitting layer 15 b is approximately 1.6 to 1.9.Thus, to reduce dependence on the viewing angle, the opticalinterference layer 12 is desirably made of a transparent material havinga high refractive index, such as titanium oxide (TiO₂), niobium oxide(Nb₂O₃), zirconium oxide, silicon nitride (SiN), zinc oxide (ZnO),molybdenum oxide (MoO₃), ITO, IZO, zinc sulfide (ZnS), or zinc selenide(ZnSe), used either singly or in combination of two or more. The opticalinterference layer 12 having a higher refractive index than therefractive index of the light emitting layer 15 b is provided so thatthe dependence of the display apparatus on the viewing angle is reduced.When the refractive index of the optical interference layer 12 is higherthan the refractive index of the light emitting layer 15 b, therefraction angle of light traveling from the light emitting layer 15 btoward the substrate 10 is smaller than the incident angle of the light.This is expected to produce an advantage that an effect of an outgoingangle from the light emitting layer 15 b on reflection light reflectedfrom the reflection layer 11 is minimized. Further, a material having ahigher refractive index is more likely to have lower wavelengthdispersibility (nr/nb). The optical interference layer 12 can be made ofan organic material that satisfies the above-described refractive indexcondition. The optical interference layer 12 can also be made of amaterial with a refractive index adjusted to satisfy the above-describedrefractive index condition by changing the composition of the materialor by combining different materials. While the optical interferencelayer 12 can be a conductive layer because the optical interferencelayer 12 can be divided by patterning between pixels, the opticalinterference layer 12 is desirably an insulating layer from thestandpoint of production because it is only necessary to form theoptical interference layer 12 entirely and uniformly and no patterningis needed.

According to the present exemplary embodiment, as described above, theoptical distance from the light emitting layer 15 b to the reflectionlayer 11 is adjusted such that the orders of interference m of (2m+1)λ/4in the blue, green, and red wavelength regions are respectively 5, 4,and 3. Specifically, the optical distance is adjusted to obtain(11/4)λr, (9/4)λg, and (7/4)λb. It should be noted that an error ofapproximately λ/8 is allowed in each optical distance. This conditionand the above-described refractive index condition of the opticalinterference layer 12 are satisfied so that color shifts caused by achange in viewing angle are reduced.

The thickness of the optical interference layer 12 can be adjusted basedon the thickness of the pixel electrode 13 and the thickness of theorganic layer 15. The total physical thickness of the opticalinterference layer 12 and the pixel electrode 13 is adjusted to 400 nmto 600 nm so that the physical thickness of the organic layer 15 becomes200 nm or smaller. This is desirable because an increase in drivingvoltage of the light emitting elements 2 can be prevented.

The organic layer 15 is a layer including at least the light emittinglayer 15 b which emits white light. While the light emitting layer 15 bcan be configured such that two materials including a blue lightemitting dopant and a yellow light emitting dopant simultaneously emitlight, the light emitting layer 15 b is desirably configured such thatthree materials including a blue light emitting dopant, a green lightemitting dopant, and a red light emitting dopant simultaneously emitlight. The light emitting layer 15 b can have a single- or multi-layerstructure. In the case of the single-layer structure, the light emittinglayer 15 b can be prepared by quaternary vapor deposition of fourmaterials including a host material of the light emitting layer 15 b andred, green, and blue light emitting dopants. In the case of themulti-layer structure, the light emitting layer 15 b can have atwo-layer structure including a yellow light emitting layer with red andgreen light emitting dopants and a blue light emitting layer, or athree-layer structure including red, green, and blue light emittingdopants. Further, in the case of the multi-layer structure, anintermediate layer can be provided between light emitting layers toadjust light emission balance.

When the light emitting layer 15 b is excessively thick and has a widelight emission distribution, or when the light emitting layer 15 bincludes a plurality of layers each emitting a different color and thelight emitting layers are separated from each other by a distance of 50nm or greater, a deviation from optical interference design can occur tocause a decrease in emission efficiency and/or a decrease in colorpurity. Thus, the thickness of the light emitting layer 15 b isdesirably adjusted to 50 nm or smaller, or the total light emittingregion of the light emitting dopants of the respective colors isdesirably adjusted to 50 nm or smaller. Further, in the case of thelight emitting layer 15 b having a multi-layer structure, the blue lightemitting layer of the light emitting layer 15 b is desirably situated onthe upper electrode 16 side. More desirably, the red light emittinglayer, the green light emitting layer, and the blue light emitting layerare stacked in this order from the reflection layer 11 side, from thestandpoint of interference design.

The color filter 18 can be adjusted to optimize the transmittance foreach color in order to obtain desired color purity.

Further, while FIG. 1 illustrates the structure according to theexemplary embodiment in which three-color pixels including the bluepixel 1B, the green pixel 1G, and the red pixel 1R are used to realize afull-color display, a white pixel can also be included in addition tothe three-color pixels according to another exemplary embodiment. Inthis case, a filter of the color filter 18 that corresponds to the whitepixel can be transparent. Being transparent indicates that the filtertransmits light of every one of the red, green, and blue wavelengthregions. Invisible light such as infrared light can be eithertransmitted or not transmitted. The white pixel is included in additionto the red, green, and blue pixels so that the power consumption can befurther reduced.

The display apparatus according to an exemplary embodiment is for use ina television, a monitor of a personal computer (PC), a display unit ofan image capturing apparatus, a display unit of a mobile phone, a carmonitor, etc. Examples of the image capturing apparatus include adigital camera, and the display unit of the image capturing apparatuscan be a display unit on the back side or a display unit stored in anelectronic view finder (EVF), etc.

The image capturing apparatus including the display apparatus accordingto the exemplary embodiment can further include an active elementconnected to the display apparatus, an optical unit including aplurality of lenses, and an image capturing element configured toreceive light transmitted through the optical unit. The displayapparatus can display images captured by the image capturing element.

The display unit of the mobile phone can be a display unit having adisplay function only or a display unit further including anidentification unit configured to identify positional coordinates. Thepositional coordinate identification unit can be a capacitance sensor.

The car monitor can be a monitor configured to display images to be usedfor checking an area surrounding the car or a monitor which shows astate such as the speed of the car.

In the following examples, optical characteristics of the displayapparatus illustrated in FIG. 1 were evaluated by simulation. Theorganic layer 15 of the light emitting element 2 included a holetransporting layer, light emitting layers A and B, and an electrontransporting layer in this order from the substrate 10 side. Thereflection layer 11 was an aluminum layer having a thickness of 100 nm.The pixel electrode 13 was an IZO layer having a thickness of 50 nm. Thethickness of the hole transporting layer of the organic layer 15 was 110nm. The light emitting layer A was a green and red light emitting layer,and the thickness of the light emitting layer A was 10 nm. The lightemitting layer B was a blue light emitting layer, and the thickness ofthe light emitting layer B was 10 nm. The thickness of the electrontransporting layer was 40 nm. Further, the light emitting positions ofthe light emitting layers A and B were respectively on the upperelectrode 16 side. The upper electrode 16 was a Ag layer with athickness of 10 nm. The transparent sealing film 17 was a SiN film witha thickness of 2000 nm, and an upper part of the transparent sealingfilm 17 was a resin layer (not illustrated). An EL spectrum emitted tothe resin layer was calculated in the simulation.

The EL spectrum was simulated by setting a case in which the lightemitting dopants of the respective colors in the light emitting layers Aand B emit the same number of photons, and combining the fluorescentspectra of the light emitting dopants with resonance effects acquired bysimulation.

FIG. 3 illustrates the fluorescent spectra of the light emitting dopantsthat were used. Further, the obtained EL spectrum is combined with eachspectroscopic characteristic of the color filter 18 (FIG. 5) to obtainan EL spectrum for each color pixel. From the EL spectrum for each colorpixel, National Television System Committee (NTSC) coverage, colorreproduction range, and power consumption were evaluated. The NTSCcoverage is a value obtained by calculating the International Commissionon Illumination (CIE) 1931 (x, y) chromaticity from the EL spectrum ofeach color pixel and dividing the area of a region where a triangleformed by the NTSC values overlaps a triangle formed by the calculatedchromaticity values of the respective colors by the area of the triangleformed by the NTSC values. The NTSC values were blue (0.14, 0.08), green(0.21, 0.71), and red (0.67, 0.33). Further, as to the powerconsumption, a luminance ratio at the time of producing white (0.31,0.33) of predetermined luminance was calculated based on the red, green,and blue chromaticity values obtained for each color pixel, and thepower consumption was estimated with the voltage being constant.Further, as to the viewing angle dependence, a case of radiation from aninternal light emitting point in an oblique direction at θ=20° withrespect to a front direction at an angle θ=0° was simulated, and colorshifts in the front direction and the oblique direction were evaluatedto evaluate the viewing angle dependence based on a change in the colorreproduction range.

Optical constants of materials that were used in the simulation are fromdata obtained by spectroscopic ellipsometry measurement or fromliterature data.

In a first comparative example, the optical interference layer 12 was aSiN layer with a thickness of 570 nm. The orders of interference m forblue (λb=460 nm), green (λg=530 nm), and red (λr=630 nm) wererespectively 6, 5, and 4. In other words, evaluations were performed forthe orders of interference that are one order higher than thoseaccording to the exemplary embodiment. Specifically, this is a conditionunder which the optical distances from the light emitting layers A and Bto the reflection layer 11 are (13/4)λb, (11/4)λg, and (9/4)λr. As tooptical characteristics of SiN, a refractive index n450 at a wavelengthof 450 nm was 1.99, and the ratio (n650/n450) of a refractive index n650at a wavelength of 650 nm to the refractive index n450 was 0.98. FIG. 5illustrates EL spectra of light emitted to the resin layer at aninternal light emitting angle θ=0° and 20°.

The NTSC coverage according to the first comparative example was 93.8%in the front direction and 67.0% in the oblique direction, which is asignificant drop. Further, the NTSC ratio also dropped. The drops werecaused by color shifts due to significant shifts of blue and green lightemission peaks to shorter wavelengths. For example, in green pixels, redlight leaks easily from the green filter 18G, and in blue pixels, greenlight leaks from the blue filter 18B. In second and third comparativeexamples and a first example below, the power consumption is specifiedrelative to the power consumption in the first comparative example whichis defined as 1.

In the second comparative example, a similar structure to the structureaccording to the first comparative example, except that the thickness ofthe SiN layer as the optical interference layer 12 was 440 nm, wasevaluated. The optical distances from the light emitting layers A and Bto the reflection layer 11 were (11/4)λb, (9/4)λg, and (7/4)λr forλb=460 nm, λg=540 nm, and λr=670 nm. FIG. 6 illustrates the obtained ELspectrum.

The NTSC coverage in the second comparative example was 89.8% in thefront direction and 93.2% in the oblique direction, and color shiftscaused by the viewing angle were reduced. However, the power consumptionin the front direction was 1.40, which is greater than the powerconsumption of 1 in the first comparative example. This is due to lowwavelength dispersibility, as the ratio (n650/n450) indicating thewavelength dispersibility of the SiN layer which is the opticalinterference layer 12 is 0.98. Thus, multi-mode resonance peaks coincideat a higher wavelength than 650 nm to cause a decrease in red luminancein a low visual sensitivity region.

In the third comparative example, a similar structure to the structureaccording to the first comparative example, except that the opticalinterference layer 12 with a thickness 490 of nm was formed using anorganic material (Org1) having a smaller refractive index than the lightemitting layers A and B, was evaluated. The orders of interference m forblue (λb=465 nm), green (λg=543 nm), and red (λr=658 nm) wererespectively 5, 4, and 3. This is a condition under which the opticaldistances from the light emitting layers A and B to the reflection layer11 are (11/4)λb, (9/4)λg, (7/4)λr. As to the optical characteristics ofthe organic material Org1, the refractive index n450 at the wavelengthof 450 nm was 1.86, and the ratio (n650/n450) of the refractive indexn650 to the refractive index n450 at the wavelength of 650 nm was 0.92.FIG. 7 illustrates the obtained EL spectrum.

The NTSC coverage according to the third comparative example was 91.1%in the front direction and 82.3% in the oblique direction, and a colorshift occurred in the oblique direction. This is due to a lowerrefractive index of the optical interference layer 12 than therefractive indexes of the light emitting layers A and B. Further, thepower consumption in the front direction was 1.17 with respect to thepower consumption of 1 in the first comparative example.

In the first example, a similar structure to the structure according tothe first comparative example, except that the optical interferencelayer 12 was a titanium oxide (TiO₂) layer with a thickness of 368 nm,was evaluated. As to the optical characteristics of TiO₂ used, therefractive index n450 at the wavelength of 450 nm was 2.44, and theratio (n650/n450) of the refractive index n650 at the wavelength of 650nm to the refractive index n450 was 0.91. The orders of interference mfor blue (λb=460 nm), green (λg=535 nm), and red (λr=655 nm) wererespectively 5, 4, and 3. Specifically, this is a condition under whichthe optical distances from the light emitting layers A and B to thereflection layer 11 are (11/4)λb, (9/4)λg, (7/4)λr. FIG. 8 illustratesthe obtained EL spectrum.

The NTSC coverage according to the first example was 98.1% in the frontdirection and 92.7% in the oblique direction, and color shifts caused bythe viewing angle are reduced. Further, the power consumption in thefront direction was 1.15 with respect to 1 in the first comparativeexample, which is lower than those in the second and third comparativeexamples. This is because the ratio n650/n450 was 0.91 and, thus, thered resonance wavelength in the multi-mode resonance wavelength was inan appropriate position.

In second, third, and fourth examples, similar structures to thestructure according to the first example, except that a niobium oxide(Nb₂O₃) layer, an ITO layer, and an IZO layer, each of which is atransparent oxide layer having a high refractive index, were used as theoptical interference layer 12, were evaluated. The results are shown inTable 1.

TABLE 1 First Second Third Comparative Comparative Comparative ExampleExample Example Optical Material SiN SiN Org1 Interference Thickness 570440 490 Layer (nm) n450 1.99 1.99 1.86 n650/n450 0.98 0.98 0.92 Ordersof Interference m 6, 5, 4 5, 4, 3 5, 4, 3 (Blue, Green, Red) PowerConsumption 1 1.40 1.17 NTSC Front 93.8% 89.8% 91.1% Coverage Direction(106.0%) (107.0%) (105.7%) (NTSC θ = 0° Ratio) Oblique 67.0% 93.2% 82.3%Direction (71.1%) (101.8%) (90.0%) θ = 20° First Second Third FourthExample Example Example Example Optical Material TiO₂ Nb₂O₃ IZO ITOInterference Thickness 368 355 410 520 Layer (nm) n450 2.44 2.45 2.201.97 n650/n450 0.91 0.94 0.92 0.90 Orders of Interference m 5, 4, 3 5,4, 3 5, 4, 3 5, 4, 3 (Blue, Green, Red) Power Consumption 1.15 1.16 1.231.22 NTSC Front 98.1% 98.0% 94.5% 92.4% Coverage Direction (112.7%)(115.6%) (109.1%) (105.0%) (NTSC θ = 0° Ratio) Oblique 92.7% 92.3% 91.7%90.0% Direction (104.5%) (102.8%) (101.9%) (99.4%) θ = 20°

As shown in Table 1, in the first to fourth examples, the NTSC coverageis 90% or higher in both the front and oblique directions, and theviewing angle dependence is reduced without increasing the powerconsumption, compared to the first to third comparative examples.

The display apparatus according to the present exemplary embodiment iseasy to manufacture because all the pixels have the same structureexcept for the color filter, produces suitable resonance effects withrespect to the respective colors, and has an improved color reproductionrange and decreased viewing angle dependence without an increase inpower consumption.

While the present disclosure has been described with reference toexemplary embodiments, it is to be understood that the invention is notlimited to the disclosed exemplary embodiments. The scope of thefollowing claims is to be accorded the broadest interpretation so as toencompass all such modifications and equivalent structures andfunctions.

What is claimed is:
 1. A light emitting apparatus comprising: asubstrate; a reflection layer disposed over the substrate; an opticalinterference layer disposed over the reflection layer; a light emittinglayer disposed over the reflection layer; and an upper transparentelectrode disposed over the light emitting layer; wherein a refractiveindex of the optical interference layer is larger than that of the lightemitting layer, and wherein the optical interference layer comprises amaterial selected from the group consisting of titanium oxide, niobiumoxide, zirconium oxide, silicon nitride, zinc oxide, molybdenum oxide,indium tin oxide (ITO), indium zinc oxide (IZO), zinc sulfide, and zincselenide, and wherein a total of thickness of the optical interferencelayer and thickness of the reflection layer is 400 nm to 600 nm.
 2. Thelight emitting apparatus according to claim 1, wherein the lightemitting layer emits white light.
 3. The light emitting apparatusaccording to claim 1, wherein the light emitting layer comprises twolight emitting layers.
 4. The light emitting apparatus according toclaim 3, the two light emitting layers contact with each other.
 5. Thelight emitting apparatus according to claim 3, the total thickness ofthe two light emitting layers is 50 nm or less.
 6. The light emittingapparatus according to claim 1, wherein a ratio (nr/nb) of a refractiveindex (nr) with respect to a red wavelength region to a refractive index(nb) with respect to a blue wavelength region in the opticalinterference layer is less than 0.95, the (nr/nb) is a ratio of arefractive index at a wavelength of 650 nm to the refractive index atthe wavelength of 450 nm.
 7. The light emitting apparatus according toclaim 1, further comprising a color filter configured to transmit eachof light of a red wavelength region, light of a green wavelength region,and light of a blue wavelength region.
 8. The light emitting apparatusaccording to claim 1, wherein an optical distance from the lightemitting layer to the reflection layer is (2m+1)λ/4±( 1/16)λ, where mrepresents an order of interference and A represents light emittingwavelength.
 9. An imaging apparatus comprising: an optical unitincluding a plurality of lenses; an image sensor element configured toreceive light transmitted through the optical unit; and a displayapparatus configured to display an image obtained by the image sensorelement, wherein the display apparatus is the light emitting apparatusaccording to claim
 1. 10. A light emitting apparatus comprising: asubstrate; a reflection layer disposed over the substrate; an opticalinterference layer disposed over the reflection layer; a plurality oflower transparent electrodes disposed over the optical interferencelayer; a light emitting layer disposed over the plurality of the lowertransparent electrodes; and an upper transparent electrode disposed overthe light emitting layer; wherein the optical interference layercomprises a material selected from the group consisting of titaniumoxide, niobium oxide, zirconium oxide, silicon nitride, zinc oxide,molybdenum oxide, indium tin oxide (ITO), indium zinc oxide (IZO), zincsulfide, and zinc selenide, and wherein orders of interference m inblue, green, and red wavelength regions are 5, 4, and 3, respectively,when an optical distance from the light emitting layer to the reflectionlayer is (2m+1)λ/4±(⅛)λ, where λ represents light emitting wavelength.11. The light emitting apparatus according to claim 10, wherein thelight emitting layer emits white light.
 12. The light emitting apparatusaccording to claim 10, wherein the light emitting layer comprises twolight emitting layers.
 13. The light emitting apparatus according toclaim 12, the two light emitting layers contact with each other.
 14. Thelight emitting apparatus according to claim 12, the total thickness ofthe two light emitting layers is 50 nm or less.
 15. The light emittingapparatus according to claim 10, wherein a ratio (nr/nb) of a refractiveindex (nr) with respect to a red wavelength region to a refractive index(nb) with respect to a blue wavelength region in the opticalinterference layer is less than 0.95, the (nr/nb) is a ratio of arefractive index at a wavelength of 650 nm to the refractive index atthe wavelength of 450 nm.
 16. The light emitting apparatus according toclaim 10, further comprising a color filter configured to transmit eachof light of the red wavelength region, light of the green wavelengthregion, and light of the blue wavelength region.
 17. The light emittingapparatus according to claim 10, wherein the optical distance from thelight emitting layer to the reflection layer is (2m+1)λ/4±( 1/16)λ. 18.An imaging apparatus comprising: an optical unit including a pluralityof lenses; an image sensor element configured to receive lighttransmitted through the optical unit; and a display apparatus configuredto display an image obtained by the image sensor element, wherein thedisplay apparatus is the light emitting apparatus according to claim 10.19. The light emitting apparatus according to claim 1, furthercomprising a lower electrode disposed between the optical interferencelayer and the light emitting layer.
 20. The light emitting apparatusaccording to claim 1, the lower electrode comprises a first lowerelectrode and a second lower electrode, the first lower electrode andthe second lower electrode are separated from each other.